Secure core material for documents

ABSTRACT

Particles conveying a code are incorporated into polymer matrix to form a core document substrate. These particles may be colored to create a distinctive look of the document that makes it unique for a particular document issuer and enables visual authentication. Addition of a covert attribute to the particle, such as a UV pigment or hidden layer of material, allows a covert, forensic characteristic and it also allows a mathematical description to be calculated describing the random distribution of a specific area on a document and then captured on it (e.g., in the bar code or magnetic stripe or digital watermark on an ID document).

RELATED APPLICATIONS

The present application is a Divisional of U.S. patent application Ser.No. 12/917,355, filed Nov. 1, 2010, now U.S. Pat. No. 7,938,333, issuedMay 10, 2011, which is a Continuation of U.S. patent application Ser.No. 11/625,665, filed Jan. 22, 2007 now U.S. Pat No. 7,823,791 which isa Continuation-in-Part of U.S. patent application Ser. No. 11/236,406,filed Sep. 26, 2005 now abandoned, and claims benefit of U.S.Provisional Application No. 60/760,621, filed Jan. 20, 2006. Each of theabove U.S. patent documents is herein incorporated by reference.

BACKGROUND

As counterfeiters become increasingly sophisticated in creatingcounterfeit secure documents (either from scratch or modifying validdocuments), there is need for increasingly effective security measuresto thwart them. One way to thwart counterfeiters is to insert featuresinto documents that are difficult to reproduce. In some cases, thesefeatures are intended to be covert so that it is difficult for thecounterfeiter to even identify their presence on the document. As anadditional layer of security, these features should have a linkingrelationship with other features that interlock the features to increasethe difficulty in accurately reproducing the relationship and showevidence of tampering when the relationship is broken. The attributesidentified above are needed for a broad spectrum of secure documents,and are particularly useful in identification documents. To providecontext for security features in identification documents, a descriptionof these documents and methods for creating them follows below.

Secure Documents

Secure documents, and in particular, identification documents (hereafter“ID documents”) play a critical role in today's society. One example ofan ID document is an identification card (“ID card”). ID documents areused on a daily basis—to prove identity, to verify age, to access asecure area, to evidence driving privileges, to cash a check, and so on.Airplane passengers are required to show an ID document during check in,security screening and prior to boarding their flight. In addition,because we live in an ever-evolving cashless society, ID documents areused to make payments, access an automated teller machine (ATM), debitan account, or make a payment, etc.

For the purposes of this disclosure, ID documents are broadly definedherein, and include, e.g., credit cards, bank cards, phone cards,passports, driver's licenses, network access cards, employee badges,debit cards, security cards, smart cards (e.g., cards that include onemore semiconductor chips, such as memory devices, microprocessors, andmicrocontrollers), contact cards, contactless cards, proximity cards(e.g., radio frequency (RFID) cards), visas, immigration documentation,national ID cards, citizenship cards, social security cards, securitybadges, certificates, identification cards or documents, voterregistration cards, police ID cards, border crossing cards, legalinstruments, security clearance badges and cards, gun permits, giftcertificates or cards, membership cards or badges, etc.

Many types of identification documents carry certain items ofinformation which relate to the identity of the bearer. Examples of suchinformation include name, address, birth date, signature andphotographic image; the cards or documents may in addition carry othervariable data (i.e., data specific to a particular card or document, forexample an employee number) and invariant data (i.e., data common to alarge number of cards, for example the name of an employer). All of thecards described above will be generically referred to as “ID documents”.

FIGS. 1 and 2 illustrate a front view and cross-sectional view (takenalong the A-A line), respectively, of an identification (ID) document10. In FIG. 1, the ID document 10 includes a photographic image 12, abar code 14 (which may contain information specific to the person whoseimage appears in photographic image 12 and/or information that is thesame from ID document to ID document), variable personal information 16,such as an address, signature, and/or birthdate, and biometricinformation 18 associated with the person whose image appears inphotographic image 12 (e.g., a fingerprint, a facial image or template,or iris or retinal template), a magnetic stripe (which, for example, canbe on a side of the ID document that is opposite the side with thephotographic image), and various security features, such as a securitypattern (for example, a printed pattern comprising a tightly printedpattern of finely divided printed and unprinted areas in close proximityto each other, such as a fine-line printed security pattern as is usedin the printing of banknote paper, stock certificates, and the like).

Referring to FIG. 2, the ID document 10 comprises a pre-printed core 20(also referred to as a substrate). In many applications, the core can bea light-colored, opaque material (e.g., TESLIN (available from PPGIndustries), polyvinyl chloride (PVC) material, polyester,polycarbonate, etc.). The core 20 is laminated with a transparentmaterial, such as clear polycarbonate, PVC or polyester material 22,which, by way of example, can be about 1-10 mil thick. The composite ofthe core 20 and clear laminate material 22 form a so-called “card blank”25 that can be up to about 27 to 33 mils thick in accordance with ANSIstandards. Information 26 a-c is printed on the card blank 25 using amethod such as Laser Xerography or Dye Diffusion Thermal Transfer(“D2T2”) printing (e.g., as described in commonly assigned U.S. Pat. No.6,066,594, which is incorporated by reference). The information 26 a-ccan, for example, comprise variable information (e.g., bearerinformation) and an indicium or indicia, such as the invariant ornonvarying information common to a large number of identificationdocuments, for example the name and logo of the organization issuing thedocuments. The information 26 a-c may be formed by any known processcapable of forming the indicium on the specific core material used.

To facilitate printing of data on the card structure, an image receivinglayer is applied to the card structure prior to printing for someprinting technologies. One type of printing technology that uses animage receiving layer is D2T2 printing. U.S. Pat. Nos. 6,066,594 and5,334,573 describe image receiving layers for D2T2 printing. A sheet orlayer which is comprised of a polymer system of which at least onepolymer is capable of receiving image-forming materials from a donorsheet upon the application of heat. The polymer system of the receivingsheet or layer is incompatible or immiscible with the polymer of thedonor sheet at the receiving sheet/donor sheet interface to minimizeadhesion between the donor sheet and the receiving sheet or layer duringprinting. The polymer system of the receiving sheet or layer can besubstantially free from release agents, such as silicone-based oils,poly(organosiloxanes), fluorinated polymers, fluorine- orphosphate-containing surfactants, fatty acid surfactants and waxes.Binder materials for the dyes are immiscible with the polymer system ofthe image-receiving layer. The most common image-receiving layerpolymers are polyester, polycaprolactone and poly(vinyl chloride).Processes for forming such image-receiving layers are also described indetail in these patents; in most cases, the polymer(s) used to form theimage-receiving layer are dissolved in an organic solvent, such asmethyl ethyl ketone, dichloromethane or chloroform, and the resultantsolution coated on to the polymer layer using conventional coatingapparatus, and the solvent evaporated to form the image-receiving layer.However, if desired the image-receiving layer can be applied to thepolymer layer by extrusion casting, or by slot, gravure or other knowncoating methods.

Other forms of image receiving layers include image receiving layers forXerographic printing and inkjet printing. These image receiving layersare applied to substrates such as paper or plastic and comprisematerials that enhance reception of ink or dye to the substrate. Imagereceiving layers for Xerographic printing are sometimes referred to as“laser lock” or “toner lock.”

To protect the information that is printed, an additional layer oftransparent overlaminate 24 can be coupled to the card blank and printedinformation. Illustrative examples of usable materials for overlaminatesinclude biaxially oriented polyester or other optically clear durableplastic film.

“Laminate” and “overlaminate” include, but are not limited to film andsheet products. Laminates used in documents include substantiallytransparent polymers. Examples of laminates used in documents includepolyester, polycarbonate, polystyrene, cellulose ester, polyolefin,polysulfone, and polyamide. Laminates can be made using either anamorphous or biaxially oriented polymer. The laminate can comprise aplurality of separate laminate layers, for example a boundary layerand/or a film layer.

The degree of transparency of the laminate can, for example, be dictatedby the information contained within the identification document, theparticular colors and/or security features used, etc. The thickness ofthe laminate layers can vary and is typically about 1 -20 mils.Lamination of any laminate layer(s) to any other layer of material(e.g., a core layer) can be accomplished using known laminationprocesses.

In ID documents, a laminate can provide a protective covering for theprinted substrates and a level of protection against unauthorizedtampering (e.g., a laminate would have to be removed to alter theprinted information and then subsequently replaced after thealteration). Various lamination processes are disclosed in assignee'sU.S. Pat. Nos. 5,783,024, 6,007,660, 6,066,594, and 6,159,327. Otherlamination processes are disclosed, e.g., in U.S. Pat. Nos. 6,283,188and 6,003,581, A co-extruded lamination technology appears in U.S.patent application Ser. No. 10/692,463. Each of these U.S. patents andapplications is herein incorporated by reference.

The material(s) from which a laminate is made may be transparent, butneed not be. Laminates can include synthetic resin-impregnated or coatedbase materials composed of successive layers of material, bondedtogether via heat, pressure, and/or adhesive. Laminates also includessecurity laminates, such as a transparent laminate material withproprietary security technology features and processes, which protectsdocuments of value from counterfeiting, data alteration, photosubstitution, duplication (including color photocopying), and simulationby use of materials and technologies that are commonly available.Laminates also can include thermosetting materials, such as epoxy.

Manufacture Environments

Commercial systems for issuing ID documents are of two main types,namely so-called “central” issue (CI), and so-called “on-the-spot” or“over-the-counter” (OTC) issue.

CI type ID documents are not immediately provided to the bearer, but arelater issued to the bearer from a central location. For example, in onetype of CI environment, a bearer reports to a document station wheredata is collected, the data are forwarded to a central location wherethe card is produced, and the card is forwarded to the bearer, often bymail. Another illustrative example of a CI assembling process occurs ina setting where a driver renews her license by mail or over theInternet, then receives a drivers license card through the mail.

A CI assembling process is more of a bulk process facility, where manycards are produced in a centralized facility, one after another. (Forexample, picture a setting where a driver passes a driving test, butthen receives her license in the mail from a CI facility a short timelater. The CI facility may process thousands of cards in a continuousmanner).

Centrally issued identification documents can be produced from digitallystored information and generally comprise an opaque core material (alsoreferred to as “substrate”), such as paper or plastic, sandwichedbetween two or more layers of clear plastic laminate, such as polyester,to protect the aforementioned items of information from wear, exposureto the elements and tampering. U.S. Pat. No. 6,817,530, which is herebyincorporated by reference, describes approaches for manufacturingidentification documents in a central issue process.

In contrast to CI identification documents, OTC identification documentsare issued immediately to a bearer who is present at a document-issuingstation. An OTC assembling process provides an ID document“on-the-spot”. An example of an OTC assembling process is a Departmentof Motor Vehicles (“DMV”) setting where a driver's license is issued toa person, on the spot, after a successful exam. In some instances, thevery nature of the OTC assembling process results in small, sometimescompact, printing and card assemblers for printing the ID document.

OTC identification documents of the types mentioned above can take anumber of forms, depending on cost and desired features. Some OTC IDdocuments comprise highly plasticized poly(vinyl chloride) or have acomposite structure with polyester laminated to 0.5-4.0 mil(13-104.mu.m) poly(vinyl chloride) film on the outside of typical PVC orComposite cards, which provides a suitable image receiving layer forheat transferable dyes which form a photographic image, together withany variant or invariant data required for the identification of thebearer. These data are subsequently protected to varying degrees byclear, thin (0.125-0.250 mil, 3-6.mu.m) overlay patches applied at theprinthead, holographic hot stamp foils (0.125-0.250 mil 3-6.mu.m), or aclear polyester laminate (0.5-10 mil, 13-254.mu.m) supporting commonsecurity features. These last two types of protective foil or laminatesometimes are applied at a laminating station separate from theprinthead. The choice of laminate dictates the degree of durability andsecurity imparted to the system in protecting the image and other data.One form of overlay is referred to as a “transferred panel” or“O-panel,”. This type of panel refers to a panel in the print ribbonthat is transferred to the document with the use of the printhead.

SUMMARY

The invention provides security features for secure documents, includingfeatures that enable verification. The invention also provides methodsfor making the security features, document structures including thesefeatures, and methods for evaluating these features in suspectdocuments.

One aspect of the invention is a secure document core materialcomprising a synthetic printing material such as polyolefin or silicafilled polyolefin, a non-reactive absorbent material distributed in thesynthetic printing material, and a covert material adhering to particlesof the absorbent material. One example of the absorbent material isclay, and an example of the covert material is a pigment that isdetectable in response to non-visible light illumination, such as afluorescing UV pigment.

Another aspect of the invention is a secure document. The document has asynthetic core comprising a polymer and a non-reactive absorbentmaterial distributed in the polymer. A covert material adheres toparticles of the absorbent material. In particular, for example, acovert pigment is adheres to particles of clay that are distributedwithin the polymer.

In one embodiment of the secure document, the covert material has adistribution within the synthetic core that is readable by scanning thesecure document with an illumination source. A representation of thedistribution is encoded in a machine readable data carrier within thesecure document. This relationship between attributes of the care andthe machine readable data enables automated authentication by scanningan image of the document (e.g., with a non-visible light source),computing a representation of the distribution from the scanned image,and comparing it with the representation in the machine readable datacarrier.

Yet another aspect of the invention is a method of making a securesynthetic print media. The method includes mixing clay particles with acovert pigment such that the covert pigment adheres to the clayparticles, and mixing the clay particles into a synthetic print mediamaterial.

Another aspect of the invention is a document core material comprising acore of polyolefin, synthetic paper or print substrate, and particlesdispersed in this core, the particles each comprising layers ofmaterial, the particles having at least one visible color such that thedispersed particles provide a visibly verifiable authenticationattribute for the core material, and the particles having a non-visibleforensic material.

Another aspect of the invention is a secure document comprising asynthetic core, the synthetic core comprising a polymer and particlesdistributed in the polymer, the particles comprising two or more layers;and a covert material conveyed in one or more of the layers of theparticles.

Another aspect of the invention is a method of making a secure syntheticprint media comprising: providing particles having two or more layers,at least one layer conveying a visible out of gamut color and a covertlayer conveying a material visible with non-visible illumination; andmixing the particles into a synthetic print media material.

Additional inventive features include methods and systems forauthenticating documents, and in particular, methods for authenticatingdocuments made with the materials and methods described in thisdocument.

Additional features will become apparent with reference to the followingdetailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages, features, and aspects of embodiments of the inventionwill be more fully understood in conjunction with the following detaileddescription and accompanying drawings, wherein:

FIG. 1 is an illustrative example of an identification document;

FIG. 2 is an illustrative cross section of the identification documentof FIG. 1, taken along the A-A line;

FIG. 3 is a diagram illustrating a cross section of a synthetic printmedia with covert material distributed in it;

FIG. 4 is a diagram illustrating a secure document made using the securecore material of FIG. 3;

FIG. 5 is a flow diagram illustrating a method for making a secure printmedia; and

FIG. 6 is a flow diagram illustrating a method for authenticating adocument using a secure print media and data carrier on the document.

Of course, the drawings are not necessarily drawn to scale, withemphasis rather being placed upon illustrating the principles of theinvention. In the drawings, like reference numbers indicate likeelements or steps. Further, throughout this application, certainindicia, information, identification documents, data, etc., may be shownas having a particular cross sectional shape (e.g., rectangular) butthat is provided by way of example and illustration only and is notlimiting, nor is the shape intended to represent the actual resultantcross sectional shape that occurs during manufacturing of identificationdocuments.

DETAILED DESCRIPTION

A non-reactive but highly absorbent material, such as clay, isincorporated into a synthetic print media such as a polyolefin/silicamatrix to form a core document substrate. This absorbent material may beadded to create a distinctive look of the print media. Clay particlesare added to the print media in measured quantities at a known particlesize distribution so that the core looks substantially the same from thefront, back and side to the curious viewer. Addition of a covertmaterial, such as a UV pigment, introduces a covert characteristic intothe media. It also allows a mathematical description to be calculateddescribing the distribution of the covert material in a specific area ona document, which is then stored on a document made from the print media(e.g., a representation of the distribution stored in a machine readabledata carrier on the document such as a bar code, magnetic stripe ordigital watermark). Each document is unique by virtue of the clay'sdistribution within the document's core. The material is buried withinthe document, and the unique distribution for each document is protectedby virtue of the construction for the entire length of the document'slife. Since the activation and excitation of the UV pigmentadhered/adsorbed onto the surface will not be disturbed by wear andtear, the signature will remain constant over the life of the card.

FIG. 3 a diagram illustrating a cross section of a synthetic print media100 with covert material 102 distributed in it. In one embodiment, thesynthetic print media is ARTISYN from Daramic, LLC, which is a unit ofPolypore in Owensboro, Ky., ARTISYN synthetic paper is a silica-filled,polyolefin printing substrate. An alternative synthetic print media isTESLIN. TESLIN is the tradename for a silica-filled porous syntheticprinting sheet from PPG.

In one embodiment, a covert pigment adheres to clay particles, whichserve as a non-reactive, absorbent host material for the pigment, andthese clay particles with covert pigment attached 102 are distributedinto the polyolefin/silica matrix of the ARTISYN material to form asecure print media 100.

Initial tests show that 40 micron clay particles are suitable as hostsfor covert pigment, but the particle size and distribution may vary. Thecovert pigment in this embodiment is a UV fluorescing pigment called SC4 from Angstrom. Other covert pigments may be used as well.

As shown in FIG. 4, the secure printed media may be used to make an IDdocument. The ID document includes information and security featuressuch as a photo of the bearer 118, a security feature embedded in thephoto 120 (such as a covert or visible printing of bearer information),and other fixed and variable information 126. The secure print media ofFIG. 3 is used as a secure core 134 of the document. For example, in CImanufacturing process, the photo and security features are printed onthe secure core (e.g., by offset or Xerographic printing), and then alaminate 132 is applied over the secure core by platen press or otherlamination process. Feature 126 may be a bar code, RF ID chip, ormagnetic stripe that carries a representation of the distribution ofcovert material in the secure core. One example of the representation isa hash, such as a secure hash (e.g., MD-5, SHA) of the spatialdistribution. This representation of the distribution may be embedded ina digital watermark in the photo or other artwork on the document.

In an OTC manufacturing process, the secure core is used to create IDcard blanks, which are coated with an image receiving layer. The imagereceiving layer enables printing by an OTC printer (e.g., D2T2 printing)of variable bearer information at the point of issuance. An overlaminateis applied after D2T2 printing. Also, a transparent laminate (e.g.,polycarbonate or other laminate as noted above) may be applied to thecore before coating with a D2T2 receptor layer.

FIG. 5 is a flow diagram illustrating a method for making a secure printmedia. As shown in step 200, the method begins by mixing a covertpigment (e.g., the UV pigment noted above) with an absorbent material,namely clay particles. In methods we tested, we mixed these materials byshaking the materials as follows:

Test 1: Above 95% of clay particles had fluorescence under UV lightafter shaking 20 g of clay and 1 g of SC 4 UV pigment from Angstromtogether on a paint shaker for 3 hrs.

Test 2: About 100% of clay particles had fluorescence under UV lightafter shaking 20 g of clay and 2 g of SC 4 UV pigment from Angstromtogether on a paint shaker for 3 hrs.

Above 98% of test 2 modified particles had fluorescence under UV lightafter mixing with mineral oil (1 part modified clay and 10 parts mineraloil) for 20 minutes and then washing out mineral oil with hexanes 3times.

After preparing the clay particles with the covert material, theparticles are introduced into the print media material, namely, thepolyolefin/silica matrix prior to forming the print media material intosynthetic printing sheets (202, 204).

A representation of the distribution of the covert pigment is capturedby illuminating the material with a UV illumination source at apredetermined area on a sheet. This process is repeated for severaldifferent locations on a sheet, which each correspond to differentdocuments that the sheet is cut into (206). Due to the method of mixingthe covert material into the substrate, the spatial distribution ofpigment is expected to be random and unique for each document.

Next, the representation of the distribution is encoded so that it canbe included in the document and/or in a database for laterauthentication of the document (208). This may include filtering thespatial distribution into a binary sequence representing locations wherethe pigment is present or absent, hashing the sequence with a securehash, and performing further error correction or data robustness coding(e.g., spread spectrum modulation, repetition coding, etc.). Next, theencoded representation is embedded on the document (210), preferably ina machine readable data carrier.

The encoded representation may be carried in a machine readable datacarrier such as a digital watermark, RF chip, bar code, magnetic stripe,optical media, etc. A digital watermark may be steganographicallyembedded in the photo or background image of an ID document usingtechniques described in U.S. Pat. Nos. 6,122,403 and 6,614,914, whichare hereby incorporated by reference.

FIG. 6 is a flow diagram illustrating a method of verifying a documentbased on the relationship between a unique distribution of the covertmaterial in the core and its representation stored in the document. Thismethod begins by illuminating the document with a radiation source thatmakes the covert pigment detectable (300). In the case of a UVfluorescing pigment, the illumination is in a band that causes thepigment to fluoresce. An image is captured of the document in this state(302).

A representation of the covert material distribution is computed in asimilar manner as done for its original encoding (304). The storedrepresentation is read from the document (or database entry which isreferenced by an index on the document) (306). Additional inter-relatedinformation may be obtained from data elsewhere in the document (such asin chips, digital watermarks, bar codes magnetic stripes, OCR, etc.) andfrom a database indexed by an identifier carrier on the document.

Finally, this data is validated by evaluating the relationship betweenthe various data read from and derived from the document and thedatabase (308). This evaluation may include a comparison of numbers, acomparison of extracted patterns, evaluation of a hash derived fromdocument attributes to a hash stored in the document, attempteddecryption of data in the document based on a key derived from thedocument or database, etc. If the evaluation establishes that therelationship among the data elements is valid, the document is deemed tobe valid.

Another type of particle for making a unique core material is amicroparticle or security fiber. These particles may be dispersed withinthe core in addition to or as an alternative to the absorbent particlesdescribed above. One commercially available form of a microparticle is aMICROTAGGANT® identification particle from Microtrace, Inc. ofMinneapolis, Minn. For more information on these particular types ofidentification particles, see U.S. Pat. Nos. 6,309,690, 4,390,452 and4,053,433, which are hereby incorporated by reference.

In one implementation, the particles are associated with a particulardocument source, such as an issuer of identification codes. Theparticles are associated with the source by carrying a code representedas a sequence of distinct readable layers with properties such as color,visible in the UV, IR spectrum, magnetic, or thermachromic. Theseproperties can be introduced by putting pigments or dyes having theseproperties in selected layers in a particular sequence. Looking beyondthe particle itself, the core material may have a composite codecomprised of the sub-codes from the different particle types within it.For example, the composite code is further represented through theconcatenation of codes or code sequences for each of the particle typeswithin the core material. The composite code is also represented anddifferentiated from other composite codes in the distribution andorientation of the different particle types in the core material.Different particle types, such as clay and taggant particles may be usedin combination in ratios by volume of core material specificallyassociated with a document issuer, for instance.

One method to construct particles with a desired code sequence is asfollows. Each element of the code sequence is associated with aparticular color or property. The particle is then constructed inlayers. In particular in one embodiment, a layered structure isconstructed by sequentially layering coatings, each with differentpigments in the coating. One particular form of coating is a UV curableacrylic coating. After two or more stages of applying and curing thesecoatings, the layered structure is a highly crosslinked material withthermoset properties. This layered structure is cryogenically groundinto particles, which are then separated into desired sizes with asieving method. Each of the particles carries a coded sequencecorresponding to the layers.

A particular property of an element in the code sequence such as adesired color may be created by applying a dye to a side of a layer.

Particles made by this process have a platelet shape, meaning that theyhave a length and width in the X and Y plane substantially greater thanthe thickness in the Z direction. For example, the particles havelengths and widths on the order of mils and thickness on the order of afew microns. This enables the particles to line up along an orientationin the X and Y plane, with top layer forming one large face, and abottom layer forming another large face parallel to the X and Y planeand the thickness in the Z direction transverse to the top, bottom andintervening layers. The particles disperse in a core material with thisorientation, which enables the manufacture to construct a core withdesired colors (based on selection of the colors of the layers) andadditional covert properties (based on the selection of covertattributes such as only visible in UV or IR light and internal layersmade covert by the obscuring coverage of surrounding layers). Thesecovert features provide non-visible forensic attributes that can be usedto verify the authenticity of a document and/or trace it to a particularsource.

These particles are then integrated into the core material during itsmanufacture. One such manufacturing process is as follows. The particlesare mixed with a core material comprising a high molecular weightpolyolefin such as polyethylene (e.g., HDPE) in a mixing vesseloperating with high sheer and torque. Mineral oil or suitablelubricating agent and high surface area silica (25 to 30%) are mixedwith the polyolefin.

The mixture is extruded through an extrusion die to form a film of thecore material. In one embodiment of the process, a roll process is usedin which a sheet of the extruded film is passed through a counter flowbath of chlorinated solvent to extract the oils from the sheet. In oneimplementation, a three roll nip roll to roll machine transfers a 4 footwide sheet at rate of about 100-150 feet through the solvent bath. Thesolvent is dried out and collected. The extraction of the oil from thesheet leaves a void volume (e.g., 25% air). The microvoids formed by theextracted oil combined with the high surface area silica create a coresheet that serves as a print media to receive printing by a variety ofprint methods, such as those referred to in this document for making IDdocuments.

In a final stage, the sheets of core material are tempered by slowlyheating and holding at a temperature for a predetermined time period inan annealing process.

The dispersion of the particles in the polyolefin is such that ID cardscut from the sheet have a random arrangement of particles unique to thecard. The cards are amenable to authentication using the authenticationmethods described above. In particular, this random arrangement isscanned from the ID document at the time of creation or issuance andloaded into a database entry associated with the document and/or storedon a machine readable data carrier on the document. In one embodiment ofthis approach, a numerical representation of the positions of theparticles is coded into a string of numbers and hashed (e.g., through acryptographic hash), with the hash stored in the data carrier on thedocument and/or in a database referenced by a document identifier on thedocument.

A digital watermark is a particularly suitable candidate for carrying arepresentation of the pattern or the identifier that references thedatabase entry where the representation of the pattern is stored. Thedigital watermark is also particularly suitable for carrying the codesequence of the particle or the composite code sequence comprised of thecodes of different particle types in the core material. The digitalwatermark can be combined into other security elements on one or morelayers of the ID document, including laminate layers and the core layeritself. In particular, it can be embedded in background art, a photo, orsecurity element like a hologram. The watermark signal can be conveyedin images marked by thermal transfer, ink jet, laser marking, etc. onthe one or more layers of the ID document.

In addition, the selected colors of the particles gives the corematerial a unique color or colors, visible from different directions,which can be uniquely assigned to a particular issuer. One approach isto select an out of gamut color or colors for the particles and placethem in a substantially white or off white core material like apolyolefin. This gives the white or off white core material a cast inthe color of the particles carried within it. An out of gamut color isone that is not accurately reproducible by standard image scanningequipment, such as typical RGB scanners. The advantage of an out ofgamut color is that it provides yet another authentication featurebecause attempts to reproduce the color with standard scanning equipmentwill yield a different color, with a detectable difference from the outof gamut color assigned to authorized issuer of the document.

The size of the particle can vary depending on the size of the corematerial. For a 10 Mil thick core layer, the particle size is preferably5 to 10 Mil in the X-Y plane. The top and bottom faces of the particlecan then be visible in the front and back of the 10 Mil film corematerial, and in some cases from its edge, as some particles align inthe Z direction, where the core film is parallel with the X-Y plane andits edge is in the Z direction.

The use of particles in the core create a variety of ways toauthenticate the core material. One is visual inspection of the core forthe characteristic color conveyed in the particles relative to theneutral color of the host core material. Another approach is to checkfor a color shift in the core material due to inaccurate reproduction ofthe out of gamut color. Another is to read the code sequence orcomposite code sequence of the particles by image analysis or otherforensic analysis of the core material. This code sequence can be readautomatically by image scanning, with illumination in the proper bands,such as UV, IR, and white light. It can also be read through extractionof the particles and forensic analysis. Another approach is to check forthe pattern of particles in the core material that has been recorded onthe document or in a database. Combinations of two or more of theseapproaches may be used.

The code sequence can be uniquely associated with a particular documentissuer, document source or manufacturing lot. The code sequence can beused to trace a document back to its manufacturing lot, source, and/orissuer.

In alternative embodiments, the particles described above are dispersedin different forms of synthetic print substrates or synthetic paper.Additional examples include polypropylene based synthetic paper,including foamed, extruded polypropylene.

In alternative embodiments, particles are dispersed in other documentlayer materials. In one embodiment, the particles are dispersed inextruded polymer material that forms the core layer of an identificationdocument. Examples of polymer materials include polyester,polycarbonate, PVC, as well as blends of these materials, such as, inparticular, a polycarbonate and polyester blend. One method ofincorporating the particles in the core material is throughmasterbatching the particles into the polymer prior to extrusion. In oneparticular embodiment, for example, the particles are masterbatched inone material that is then coextruded with one or more additional layersto form a multilayer structure. Particles with different covert andvisible attributes may be masterbatched into different materials, whichare then coextruded to form a multilayer structure with a uniquecombination of particles. In one particular embodiment, particles of thetype described above are masterbatched into a core material ofpolycarbonate or polycarbonate/polyester blend, which is then coextrudedwith outer layers of an amorphous polyester to form a coextrudeddocument core material. Image receiving layers are optionally applied tothe core to make it receptive to inks or toners used to print additionalinformation on the document. Such layers may be applied as coatings orlaminated layers as described above.

Concluding Remarks

Having described and illustrated the principles of the technology withreference to specific implementations, it will be recognized that thetechnology can be implemented in many other, different, forms, and inmany different environments.

The technology disclosed herein can be used in combination with othertechnologies. Also, instead of ID documents, the inventive techniquescan be employed with product tags, product packaging, labels, businesscards, bags, charts, smart cards, maps, labels, etc. The term IDdocument is broadly defined herein to include these tags, maps, labels,packaging, cards, etc.

It should be understood that, in the Figures of this application, insome instances, a plurality of method steps may be shown as illustrativeof a particular method, and a single method step may be shown asillustrative of a plurality of a particular method steps.

It should be understood that showing a plurality of a particular elementor step is not intended to imply that a system or method implemented inaccordance with the invention must comprise more than one of thatelement or step, nor is it intended by illustrating a single element orstep that the invention is limited to embodiments having only a singleone of that respective elements or steps.

In addition, the total number of elements or steps shown for aparticular system element or method is not intended to be limiting;those skilled in the art will recognize that the number of a particularsystem element or method steps can, in some instances, be selected toaccommodate the particular user needs.

To provide a comprehensive disclosure without unduly lengthening thespecification, applicants hereby incorporate by reference each of theU.S. patent documents referenced above.

The technology and solutions disclosed herein have made use of elementsand techniques known from the cited documents. Other elements andtechniques from the cited documents can similarly be combined to yieldfurther implementations within the scope of the present invention.

Thus, the exemplary embodiments are only selected samples of thesolutions available by combining the teachings referenced above. Theother solutions necessarily are not exhaustively described herein, butare fairly within the understanding of an artisan given the foregoingdisclosure and familiarity with the cited art. The particularcombinations of elements and features in the above-detailed embodimentsare exemplary only; the interchanging and substitution of theseteachings with other teachings in this and the incorporated-by-referencepatent documents are also expressly contemplated.

In describing the embodiments of the invention illustrated in thefigures, specific terminology is used for the sake of clarity. However,the invention is not limited to the specific terms so selected, and eachspecific term at least includes all technical and functional equivalentsthat operate in a similar manner to accomplish a similar purpose.

1. A method of verifying, comprising: providing a secure identificationdocument, the secure identification document being made by: mixing anon-reactive material with a covert material to form a plurality ofparticles; blending the plurality of particles within a substratepolymer material to form a random distribution; capturing arepresentation of the random distribution; and embedding therepresentation in a machine readable data carrier within the secureidentification document; reading the random distribution of theplurality of particles embedded within the secure identificationdocument; deriving a representation of the read random distribution;reading at least a portion of data stored in the machine readable datacarrier within the secure identification document; comparing the derivedrepresentation with the read data; and verifying the secureidentification document if the derived representative matches the readdata.
 2. The method of claim 1, further comprising: encoding therepresentation before embedding.
 3. The method of claim 1, wherein thesubstrate polymer material is a polyolefin/silica matrix.
 4. The methodof claim 1, wherein the non-reactive material is clay.
 5. The method ofclaim 1, wherein the covert material is a UV pigment.
 6. The method ofclaim 1, wherein the random distribution of the plurality of particlesremains constant over a usage life of the secure identificationdocument.
 7. The method of claim 1, wherein the representation is amathematical description.
 8. The method of claim 1, wherein themathematical description is a hash.
 9. The method of claim 1, whereinthe machine readable data carrier comprises at least one of a bar code,a magnetic stripe, a digital watermark, a RF chip, and an optical media.10. The method of claim 1, further comprising an image receiving layeradjacent to at least one surface of the substrate.
 11. The method ofclaim 1, further comprising a laminate layer.